Ch. 2 Light and Photosynthesis (Ps)

Light Radiant energy (electromagnetic radiation) –Particle + wave Particle: torp

Light Wave: has Wavelength inversely

Light Visible light: nanometers (nm) (nano=10 -9 )

Electromagnetic spectrum T/F: Plants green because chlorophyll absorbs green light

Electromagnetic spectrum nm: Photosynthetically Active Radiation (PAR) –Drives Ps –Green least (why leaves green) Action spectrum for photosynthesis (Ps)

Radiation Helps determine IR: nm. Objects > absolute 0 emit Gain energy from IR too Pred

IR “Infrared (IR) window” of leaves Transmit near IR (beyond visible): little Most visible IR window

IR Near IR transmitted through leaves (dashed line)

IR Use IR window (sense overstory)?? First: phytochrome

Phytochrome 2 forms (interconvertible) Pr absorbs R: converted to Pfr Pfr absorbs FR (near IR): converted to Pr Pfr active

IR 1) Ratio Pr:Pfr depends on ratio R:FR light 2) R:FR influenced by leaves –Leaves remove R, let FR through “IR window”

IR Ex, red alder (Alnus rubra) Germination sensitive to Pfr –Pfr high: –Pfr low:

IR Ex, red alder (Alnus rubra) In open: lots R light, lots Pfr

IR Ex, red alder (Alnus rubra) Under canopy: lots FR light, less Pfr

IR Plants may use phytochrome –1) shaded: stimulate etiolation (spindly, less chlorophyll) –2) info on canopy (deciduous forest) Trillium

Electromagnetic spectrum UV radiation: < 350 nm (to 1 nm)

UV Danger: Damage DNA (skin cancer!) Pigments (ex, flavonoids) absorb +DNA repair mechanisms Diamorpha smallii

Units (Intensity) ?

Units

PAR: Photosynthetic Photon Flux Density (PPFD) moles photons/sq. m/sec National Mole Day??

Units PPFD 1 mole photons = 1 Einstein So, Einsteins/sq. m/sec National Mole Day??

Light intensity variation Canopies patchy in

Light intensity variation Phenoseason: seasonal light change + canopy change Max. lite ground level Max. lite canopy top

Phenoseasons Ex, Eastern Deciduous Forest understory plants 4 strategies: 1) Spring herbs (“Ea”): emerge early Canopy leaf drop Canopy leaf expansion

Spring herbs Ex, Trillium

Spring herbs Ex, Erythronium (trout lily)

2. Summer green herbs Emerge late spring, green summer, dormant fall “Us” Canopy leaf expansion Canopy leaf drop

Summer green herbs Ex, Uvularia sessilifolia (bellwort) Uvula??

Summer green herbs Ex, Uvularia sessilifolia (bellwort)

3. Late-summer herbs Emerge summer, get early fall sun (Aa) Ex, Aster acuminatus (sharp-leaved aster) Canopy leaf expansion Canopy leaf drop

4. Semievergreens Emerge late spring, green late: “Om” Ex, Oxalis montana (wood sorrel) Canopy leaf expansion Canopy leaf drop

Light variation Canopies patchy Question: Technical name for beam sunlight on forest floor?

Light variation Canopies patchy in space ______: beam sunlight on forest floor

Sunflecks: Good Useful (forest floor plants) –Some: 70% energy sunflecks

Sunflecks: Good Useful (forest floor plants) –Some: 70% energy sunflecks Ability to use: –Spring herbs (Trillium) respond –Summer green herbs (Uvularia) exploit

Sunflecks: Bad –Ex: shade-adapted Oxalis. Redwood forest ( Oxalis oregana-redwood sorrel) –Coast redwood (Sequoia sempervirens) Tallest tree: 368 ft. DBH 23 ft.!

Sunflecks: Bad O. oregana: Sunflecks damage Ps machinery

Sunflecks: Bad Sunflecks & drought stress Ex, regeneration Abies magnifica (CA red fir)

Sunflecks Ex, regeneration Abies magnifica (CA red fir) Seedling pattern from sunfleck pattern